The chemical formula of of nitric acid is HNO3.
The original structure of nitric acid will be-
HNO3
is a molecule acid hence contains one-OH group attached directly with N-atom (Central
atom), thus the structure of nitric acid molecule can be represented by the
formula (HONO2).
Spectroscopic and electron
diffraction studies have shown that HNO3 molecule in the vapour
state has trigonal planar structure with various bond angles and bond lengths.
Preparation:-
1. In the laboratory, it is prepared by heating NaNO3 or KNO3 with conc. H2SO4. Raddish brown vapours of HNO3 so produced are condensed in a water-cooled receiver.
The acid
thus produced is yellow in colour due to
the presence of NO2 formed by the decomposition of HNO3 .
Both the
structure is supported by the monobasic nature of HNO3. It may be
seen from this structures that N-atom and all three O-atoms have an octet of
electrons in their outer shell H-atom has two electrons in its shell.
Preparation:-
1. In the laboratory, it is prepared by heating NaNO3 or KNO3 with conc. H2SO4. Raddish brown vapours of HNO3 so produced are condensed in a water-cooled receiver.
The acid
thus produced is yellow in colour due to
the presence of NO2 formed by the decomposition of HNO3 .
The acid is purified by redistillation and by pasing a current of dry air or CO2 through the warm acid.
2. Manufacture:-
On a large
scale, the acid is generally prepared by Ostwald’s Process, which consist of the
following steps-
A. NH3 (N=3)obtained by Haber’s
process is oxidized to NO (N= +2) atmospheric O2 (Free from dust) in
presence of
Platinum-guaze catalyst electrically heated to 7500 C to 9000 C.
Platinum-guaze catalyst electrically heated to 7500 C to 9000 C.
Since the
reaction exothermic, heat generated in the reaction maintains the temperature
of the catalyst.
B. NO produced as above is oxidize by atmospheric O2 to NO2. Which is cooled to about 500 C and then absorbed in water (in the presence of air) to give HNO3.
B. NO produced as above is oxidize by atmospheric O2 to NO2. Which is cooled to about 500 C and then absorbed in water (in the presence of air) to give HNO3.
The usual concentrated nitric acid contains 98 % HNO3 and its specific gravity=1.5 .
Nitric acid is the most suitable catalyst, even though it is
a strongly oxidizing agent, it’s anhydrous form doesn’t react with most of the
commonly used metal powders.
Acceleration and Automation of Solid Sample Treatment
María Dolores Luque de Castro, José Luis Luque García, in Techniques and Instrumentation in Analytical Chemistry, 2002
Nitric acid
Nitric acid is the primary choice here on several grounds. It is an oxidizing acid that can dissolve most metals to form soluble metal nitrates. It has poor oxidizing strength below 2 M but is a powerful oxidizing acid in concentrated form. Its oxidizing power can be enhanced by addition of chlorate, permanganate, hydrogen peroxide or bromine, as well as by increasing its temperature and pressure. Most metals and alloys are oxidized by nitric acid; however, gold and platinum are not oxidized and some metals are passivated when attacked by concentrated nitric acid. Such metals can be dissolved by using a combination of acids or a dilute nitric solution. At temperatures in the region of 180°C, nitric acid can decompose most organic molecules, converting hydrocarbons into carbon dioxide and water.
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